Many bodily fluids can be readily identified by chemical properties such as pH. One exceptionally useful method of determining the pH of a liquid sample is through the use of an indicator, a chemical compound or combination of compounds, that has a pH dependent color. Well known examples include tea and wine. General details and descriptions of some indicators can be found, for example, in “Indicators,” E. Bishop, Pergamon Press, 1972, chapter 3.
Often an indicator is attached to a solid substrate such as paper. A sample of a liquid of which the pH needs to be determined is applied to the substrate. The pH of the liquid is determined by the color of the indicator present on the substrate. Depending on how the indicator is attached to the substrate, application of the liquid sample may cause the indicator to leach out of the substrate. Indicator leaching is undesirable and so the indicator is often substantially immobilized on the substrate.
Various medical conditions can be diagnosed by identifying the chemical and physical properties of a vaginal secretion, such as, salts of volatile amines as disclosed in U.S. Pat. No. 6,099,801. Identifying the pH of the secretions also indicates the presence of medical conditions. U.S. Pat. Nos. 5,660,790 and 5,910,447 disclose test devices for analyzing the pH of an aqueous liquid sample, however, the pH range identified by these devices is extremely narrow, namely 4.6-4.8. Moreover, the pH indicator composition is hydrophilic and thus cannot readily retain a stable indication, particularly indications requiring dehydrated environment. U.S. Pat. No. 5,468,236 discloses a disposable absorbent product comprising a chemically reactive means adapted to provide a visual indication as a result of interacting with biological fluids. The properties of the chemical means however are not defined. Moreover, the visual indication is not adapted to provide a distinct indication for a desired substance in the presence of interfering fluids.
A number of devices involving panty shields with pH indicators are known in the art, for example in U.S. Pat. Nos. 5,217,444; 5,823,953; 6,106,461 and 6,689,114. These devices can be worn by the user and whenever there is a secretion it is immediately detected by the pH indicator. U.S. Pat. No. 6,562,297 discloses an indicator bound to a hydrophilic synthetic membrane substrate and a device, such as a panty shield with an indicator bound to hydrophilic synthetic membrane substrate. A general problem, however, with these pH indicators is that they often provide “false positives” due to changes in pH on drying, interfering biological fluids and repetitive cycles of drying/wetting. Often a vaginal secretion cannot be identified with absolute certainty by an indicator due to the existence of a plurality of fluids collected with a similar pH. The “false positive” readings can be stressful and time consuming to the user. A device that minimizes these “false positive” readings is needed.
False positive readings can be caused, for example, by interfering biological fluids, such as urine. Vaginal secretions of a patient with vaginosis have a pH between 4.7 and 6.5. Because urine of a healthy patient has a pH between 5.0 and 8.0, it is very difficult to diagnose a secretion as arising from vaginosis with a high degree of confidence by just using a pH based indicator test. One solution known in the art is to sample fluid from within the vagina, where urine is not ordinarily found. This is uncomfortable and requires a visit to a health-care professional.
A second example is the identification of amniotic fluid leaking from the vagina of a pregnant woman. During pregnancy amniotic sac integrity may be compromised and a small amount of amniotic fluid may leak out through the cervix and from the vagina. If diagnosed as such, measures such as patient rest or sealing of the amniotic sack using biological glue may be prescribed. If not diagnosed the amniotic sack may later rupture causing abortion of the pregnancy, or require hospitalization of the woman and infant. If the infant is born prematurely, death or severe handicap may be a result. Extended hospitalization of the infant in an incubator is often necessary.
Due to the severe consequences of amniotic fluid leakage, pregnant women undergo severe stress and often go to a health-care professional upon secretion of any liquid from the vicinity of the vagina. The health-care professional looks for the presence of amniotic fluid by checking the pH of the vaginal secretions, amniotic fluid having a pH of between 6.0 and 8.0. Since pregnant women often have urinary incontinence and since urine typically has a pH of between 5.0 and 8.0, if only pH is checked, a false positive result may occur: urine being identified as amniotic fluid. Consequently, it is necessary that such a vaginal secretion be examined using a microscope for the presence of a fern-shaped pattern indicative of amniotic fluid.
As the time between the fluid secretion and the arrival at the health-care professional may be long, there is often no evidence of amniotic fluid upon examination. The secretion may mistakenly be assumed to be urine, often with tragic consequences. On the other hand, the healthcare professional may decide to err on the side of caution, misdiagnosing the secretion of urine as amniotic fluid leading to an unnecessary hospitalization and patient stress.
U.S. Pat. No. 6,126,597 (the '597 patent) and U.S. Pat. No. 6,149,590, (the '590 patent) a continuation-in-part of the '597 patent, are directed to a device in the form of a sanitary napkin with a pH indicator configured to identify the presence of amniotic fluid in a vaginal secretion. The '597 and '590 patents are subject to the problem of giving false positive results. The device of the '590 patent addresses this problem by further including in the device a microscope visualizable slide configured to gather a portion of a vaginal secretion. If the indicator shows the pH corresponding to that of amniotic fluid, the user presents a health-care professional with the slide. The health-care professional examines the slide with the help of a microscope for the typical fern-shaped patterns indicative of the presence of amniotic fluid.
There are a couple of disadvantages associated with this device. First, it requires that the patient visits the health-care professional to distinguish between positive and false-positives and second, a significant amount of time is lost in having the slide viewed by a professional to determine if amniotic fluid is actually leaking.
U.S. Pat. No. 5,897,834 discloses a device useful in a clinical setting for the differentiation between urine and vaginal secretions associated with vaginosis or urine and amniotic fluid. The device includes the use of indicators with a negatively charged group immobilized to a solid polymer substrate containing quaternary ammonium groups. Further the device includes a gaseous amine-releasing reagent and an amine indicator. The use of the polymer substrate containing quaternary ammonium groups is disclosed to have an advantage of sharpening the pH dependent color transition. However, these polymer substrates have been found to be less useful in non-clinical settings: the indicated pH of dried vaginal secretions is low enough to be misdiagnosed as indicating vaginosis. Thus although the device disclosed in U.S. Pat. No. 5,897,834 is useful in a clinical setting where the health care professional applies the vaginal secretion to the device and observes the color change, if integrated in a patient useable device, such as a panty shield, the device gives abundant false positive results.
There is a need for an indicator system that can differentiate between a specific biological fluid of interest and an interfering biological fluid, such as, urine. Further there is a need for a device that can distinguish between normal vaginal secretions and those associated with amniotic fluid leakage or vaginosis. Further, a system in which false positive results are minimized and a reliable indication is stable over time, while reducing the amount of time required to get the reliable result is also needed. Such a system is ideally useable by the patient to lead to greater peace of mind and to minimize unnecessary hospital visits. The characteristics of such an indicator system must not change due to long use or as a result of a wetting drying cycle and must distinguish between interfering biological fluids and minimize false positive readings. The present invention now overcomes these problems and satisfies these needs.